GLP-1 (glucagon like peptide-1) is a 30 amino acid long peptide hormone secreted by the L-cells in the intestine.
GLP-1 consists of two native forms, GLP-1 (7-36) and GLP-1 (7-37), of the following amino acid sequences:
 7   8   9  10  11  12  13  14  15  16  17His-Ala-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-18  19  20  21  22  23  24  25  26  27  28Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys-Glu-Phe-29  30  31  32  33  34  35  36Ile-Ala-Trp-Leu-Val-Lys-Gly-Arg-xwherein X is NH2 for GLP-1(7-36) and Gly for GLP-1(7-37).
GLP-1 is a so-called incretin and its primary mechanisms of actions are to:                Stimulate insulin secretion in a physiological and glucose-dependent manner        Decrease glucagon secretion        Inhibit gastric emptying        Decrease appetite        Stimulate growth/proliferation of β-cells.        
Stimulating insulin secretion and at the same time decreasing glucagon secretion is probably what makes GLP-1 a very efficient blood glucose lowering agent (1). The very efficient blood glucose lowering as well as the glucose dependency of its action makes it an ideal candidate for the treatment of Type 2 diabetes (2-10). Furthermore, it may be useful for the treatment of Type 1 diabetes in combination with insulin (11). GLP-1 offers something that no other existing drug or drug candidate can provide: very efficient blood glucose lowering, even in SU (sulphonylurea)-failures (6), without the risk of serious hypoglycaemia. Apart from these major effects, GLP-1 has also been shown to increase the rate of insulin biosynthesis (12,13) and restore the ability of the β-cells to respond rapidly to rising plasma glucose in terms of first phase insulin release in rats (14). Thus, GLP-1 would be expected to be able to prevent or delay the progression from IGT to full blown Type 2 diabetes. Patients treated with GLP-1 compared to eg metformin or sulphonylureas, will be better managed and may as a result thereof have a much later transfer to insulin requiring therapy.
Recently, GLP-1 compounds have been shown to stimulate growth and proliferation of β-cells (15-17), thereby also supporting use of GLP-1 compounds and GLP-1 agonists for increasing the number of β-cells in a patient in vivo.
An important and perhaps primary defect in Type 2 diabetes patients may be an impaired incretin function (18,19). In fact, in the rather few patients with Type 2 diabetes so far investigated for this, all had a greatly decreased or absent insulin response to the “other” incretin hormone, namely GIP (Gastric Inhibitory Polypeptide) (19,20). Because GIP is the “first-in-line” incretin and GIP signalling is defective, meal-induced insulin secretion is also defective. This cannot be overcome with endogenous or exogenous GIP because the patients are insensitive to GIP, but it may be compensated for with GLP-1 (20). In contrast to GIP, the insulinotropic action of GLP-1 is preserved in diabetic patients (21). Replacing the incretin deficiency may also be why GLP-1 treatment is so effective.
The ability of GLP-1 to decrease appetite and energy intake is now firmly established, both in normal, lean people and in obese people (22-24). Obese subjects have been shown to have an attenuated GLP-1 release in response to meals (25,26). This may further add to the potential of GLP-1 as being able to decrease weight in Type 2 diabetes patients. This use of GLP-1 is described further in WO No 98/20895 to Novo Nordisk A/S and WO No 98/28414 to Eli Lilly and Company.
GLP-1 is rapidly metabolised by the proteolytic enzyme Dipeptidyl Peptidase-IV (27) into an inactive or perhaps even antagonistic metabolite (28), complicating the use of GLP-1 as a drug.
The use of GLP-1 and analogues of GLP-1 as well as fragments thereof in the treatment of Type 1 and Type 2 diabetes and obesity are disclosed in several publications.
WO No 87/06941 and WO No 90/11296 to The General Hospital Corporation disclose GLP-1 fragments, including GLP-1(7-37) and GLP-1(7-36), and functional derivatives thereof for use as insulinotropic agents.
Furthermore, WO No 91/11457 to Buckley et al. discloses analogues of the active GLP-1 peptides 7-34, 7-35, 7-36, and 7-37 for use in the treatment of Type 2 diabetes and WO No 98/08871 to Novo Nordisk A/S discloses derivatives of GLP-1 for use in the treatment of diabetes and obesity which are especially useful as they are both metabolically stable and very potent.
However, peptides are generally not known to be orally available.
Best care for patients would obviously be achieved if a drug was orally available. The provision of orally available non-peptide GLP-1 agonists would therefore constitute a highly valuable contribution to the art.
The GLP-1 receptor is a so-called 7 transmembrane (7TM) G-protein coupled receptor. These receptors are transmembrane proteins consisting of a N-terminal extracellular part, a transmembrane core and three extracellular and three intracellular loops. The receptors are coupled to a G-protein (consisting of three subunits) and then further to an effector system. The effector system for the GLP-1 receptor is the adenylyl cyclase enzyme. Upon activation of the receptor, adenylyl cyclase catalyses the formation of the second messenger cAMP from ATP.
U.S. Pat. No. 5,670,360 to Novo Nordisk A/S discloses the cloning and use of the GLP-1 receptor. Five superfamilies of these receptors are known. Of these the glucagon-secretin (B) family consists of the receptors for GLP-1, glucagon, GIP, secretin, VIP, PACAP, calcitonin, PTH, CRF, GRF and a few more.
The (B) family is characterised by a relative large N-terminal domain of the receptor. The natural ligands for these receptors are all large peptides and the binding (and consecutive activation) of the receptors by their natural ligands is believed to involve both the N-terminal domain and the transmembrane region.
Small non-peptide agonists for peptide receptors are generally considered very difficult to find.
The above characteristics of the (B) family receptors seem to further complicate the provision of an agonist and so far no small non-peptide agonists have been described for a receptor in the (B) family.
However, surprisingly we have found a whole new class of non-peptide GLP-1 agonists which activate the human GLP-1 receptor.
They may be characterised by activating the human GLP-1 receptor without competing with GLP-1 for the GLP-1 binding site in a competition binding assay.
Furthermore, experiments have shown that the affinity of the receptor for GLP-1 changes upon incubation with some of the compounds according to the invention.
It is believed that the compounds of the invention stabilise another conformation of the receptor than that stabilised by GLP-1.
G-protein coupled receptors are theoretically thought to exist in different conformations: R and R*, where R is the inactive receptor conformation and R* the active. The most recent literature speculates that there may be one or more intermediate states (31).
One understanding of antagonists and inverse agonists is that they are able to bind to and stabilise the inactive conformation of the receptor whereas agonists bind to and stabilise the active conformation. It is not really known what a partial agonist does in these models.
The compounds according to the invention may introduce a new model in order to accommodate their characteristics. In this model we introduce a further receptor conformation R** which is another active receptor conformation.
R* would then be the conformation that GLP-1 under normal circumstances stabilises where R** is the conformation that the compounds according to the invention stabilises. A model with two different active receptor conformations may also offer an explanation for why some of the compounds according to the invention when tested in the assays are partial and not full agonists because one conformation may be able to elicit partial agonism only and the other full agonism.
Definitions
The following is a detailed definition of the terms used to describe the compounds of the invention:
“Halogen” designates an atom selected from the group consisting of F, Cl, Br or I.
The term “lower alkyl” in the present context designates a saturated, branched or straight hydrocarbon group having from 1 to 6 carbon atoms. Representative examples include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-hexyl, isohexyl and the like.
The term “lower alkenyl” as used herein represents a branched or straight hydrocarbon group having from 2 to 6 carbon atoms and at least one double bond. Examples of such groups include, but are not limited to, vinyl, 1-propenyl, 2-propenyl, isopropenyl, 1,3-butadienyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methyl-1-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 3-methyl-2-butenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 2,4-hexadienyl, 5-hexenyl and the like.
The term “lower alkynyl” as used herein represents a branched or straight hydrocarbon group having from 2 to 6 carbon atoms and at least one triple bond. Examples of such groups include, but are not limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 3-hexynyl, 5-hexynyl, 2,4-hexadiynyl and the like.
The term “lower alkanoyl” in the present context designates a group —C(O)—H or —C(O)-lower alkyl wherein lower alkyl has the above meaning. Representative examples include, but are not limited to, formyl, acetyl, propionyl, butyryl, valeryl, hexanoyl, heptanoyl and the like.
The term “cycloalkyl” as used herein represents a saturated carbocyclic group having from 3 to 10 carbon atoms. Representative examples are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and the like.
The term “cycloalkenyl” as used herein represents a carbocyclic group having from 3 to 10 carbon atoms containing at least one double bond. Representative examples are 1-cyclopentenyl, 2-cyclopentenyl, 3-cyclopentenyl, 1-cyclohexenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2-cycloheptenyl, 3-cycloheptenyl, 2-cyclooctenyl, 1,4-cyclooctadienyl and the like.
The term “heterocyclyl” as used herein represents a saturated or partially unsaturated 3 to 10 membered ring containing one or more heteroatoms selected from nitrogen, oxygen and sulfur. Representative examples are pyrrolidinyl, piperidyl, piperazinyl, morpholinyl, thiomorpholinyl, aziridinyl, tetrahydrofuranyl and the like.
The term “aryl” as used herein represents a carbocyclic aromatic ring system such as phenyl, biphenyl, naphthyl, anthracenyl, phenanthrenyl, fluorenyl, indenyl, pentalenyl, azulenyl, biphenylenyl and the like. Aryl is also intended to include the partially hydrogenated derivatives of the carbocyclic aromatic systems enumerated above. Non-limiting examples of such partially hydrogenated derivatives are 1,2,3,4-tetrahydronaphthyl, 1,4-dihydronaphthyl and the like.
The term “heteroaryl” as used herein represents a heterocyclic aromatic ring system containing one or more heteroatoms selected from nitrogen, oxygen and sulfur such as furanyl, thienyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl, isoxazolyl, isothiazolyl, 1,2,3-triazolyl, 1,2,4-triazolyl, pyranyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, 1,2,3-triazinyl, 1,2,4-triazinyl, 1,3,5-triazinyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, tetrazolyl, thiadiazinyl, indolyl, isoindolyl, benzofuranyl, benzothienyl, benzothiophenyl (thianaphthenyl), indazolyl, benzimidazolyl, benzthiazolyl, benzisothiazolyl, benzoxazolyl, benzisoxazolyl, purinyl, quinazolinyl, quinolizinyl, quinolinyl, isoquinolinyl, quinoxalinyl, naphthyridinyl, pteridinyl, carbazolyl, azepinyl, diazepinyl, acridinyl and the like. Heteroaryl is also intended to include the partially hydrogenated derivatives of the heterocyclic systems enumerated above. Non-limiting examples of such partially hydrogenated derivatives are 2,3-dihydrobenzofuranyl, pyrrolinyl, pyrazolinyl, indolinyl, oxazolidinyl, oxazolinyl, oxazepinyl and the like.
“Aryl-lower alkyl”, “heteroaryl-lower alkyl”, “aryl-lower alkenyl” etc. mean a lower alkyl or alkenyl as defined above, substituted by an aryl or heteroaryl as defined above, for example: Certain of the above defined terms may occur more than once in the structural formulae, and upon such occurrence each term shall be defined independently of the other.
Within the context of the present invention, a non-peptide is understood to refer to any chemical compound which is not a peptide. In this context a peptide is defined as a linear sequence of natural amino acids coupled by peptide bonds of a length of at least 6 amino acids including derivatives thereof wherein one or more of the amino acid residues have been chemically modified, eg by alkylation, acylation, ester formation or amide formation.
Within the context of the present invention, a GLP-1 agonist is understood to refer to any compound which fully or partially activates the human GLP-1 receptor.
Within the context of the present invention, a partial GLP-1 agonist is understood to refer to any compound which increases the activity of the human GLP-1 receptor but which compared to GLP-1 is not able to effect a full response (Emax<100% relative to GLP-1).
Within the context of the present invention, a GLP-1 antagonist is understood to refer to any compound which decreases the activity of the human GLP-1 receptor seen after stimulation with GLP-1.
Within the context of the present invention an inverse GLP-1 agonist is understood to refer to any compound which not only decreases the activity of the human GLP-1 receptor seen after stimulation with GLP-1 but also decreases the activity of the non-stimulated receptor (basal activity).
Within the context of the present invention a metabolic disorder is understood to refer to any disorder associated with the metabolism or resulting from a defect of the metabolism.
Within the context of the present invention GLP-1 is understood to refer to either or both of the above two native forms GLP-1 (7-36) and GLP-1 (7-37) unless otherwise specified.